1. Peel, core and chop the apples and place them in a saucepan, with half the cider. Bring the cider to the boil, and then cover the pan and let the apples simmer gently on a medium heat until tender.
2. Tip the apples into a blender or food processor and process them to a smooth puree. Stir in the honey and vanilla. Add half the blackberries to half the apple puree, and then process the mixture again until smooth. Sieve.
3. Heat the remaining cider until it almost boiling, then sprinkle the powdered gelatine over and stir until the gelatine has completely dissolved. Add half the gelatine and cider liquid to the apple puree and half to the blackberry puree.
4. Leave the purees to cool until almost set. Whisk the egg whites until they are stiff, then quickly fold them into the apple puree. Remove half the puree to another bowl. Stir the remaining whole blackberries into half the apple puree, and then turn this into a 1.75 litre / 3 pint / 7 1/2 cup loaf tin.
5. Top with the blackberry puree and spread it evenly. Finally, add a layer of the apple puree and smooth it evenly. To make sure the layers remain clearly separated, you can freeze each one until firm before adding the next.
6. Freeze until firm. To serve, allow to stand at room temperature for about 20 minutes to soften, then serve in thick slices, decorated with apples and blackberries.